The present invention relates generally to inhibitors for reducing or eliminating corrosion of steel by acid. More specifically, the present invention relates generally to inhibitors for reducing the corrosion of oil field chrome and carbon steels by acids.
Acid solutions are commonly used to stimulate production in oil wells, gas wells and water wells in subterranean formations. Such acid stimulations are used in conjunction with hydraulic fracturing techniques and matrix acid stimulations. In both the acid fracturing and matrix acid stimulation techniques, the well treatment acid solutions are pumped through the well casing and injected into the formation. The acid then attacks the formation and increases the permeability of the formation thereby stimulating the flow of oil, gas or water. The acids typically used include hydrochloric acid, hydrofluoric acid, acetic acid, formic acid and mixtures thereof.
In order to protect the well casing and other steel tubular goods in the well from the corrosive effects of the acid, the acid solutions typically include a corrosion inhibitor, commonly referred to as an acid corrosion inhibitor ("ACI"). Typical inhibitors include nitrogen containing compounds such as those described in U.S. Pat. No. 4,028,268, or acetylenic compounds as described in U.S. Pat. Nos. 3,779,935, 4,552,672, 4,498,997, 4,444,668 and 4,522,658. Often, mixtures of inhibitors can be employed. In addition, cinnamaldehyde may also be used, as set forth in U.S. Pat. Nos. 3,589,860 and 4,734,259.
It is also known that iodine can assist in corrosion inhibition. A combination of iodine in the acid corrosion inhibitor blend as well as potassium iodide added directly to the acid is illustrated in U.S. Pat. No. 5,543,388.
However, it is also well known that none of the currently available acid corrosion inhibitors, or their combination with elemental iodine or potassium iodide, completely stop corrosion from the commonly employed well treatment acid solutions. Furthermore, there is a well-known crosslinking incompatibility between prior art aldehyde-based acid corrosion inhibitors and polyacrylamide-based acid-gel systems. While the currently employed acid corrosion inhibitors, with or without iodine, limit corrosion, corrosion still occurs to the detriment of steel equipment installed in the wells which limits the useful life of the equipment and re-use thereof in future wells.
Accordingly, there is a need for improved acid corrosion inhibiting compositions which substantially limits corrosion of carbon and chrome steel goods when exposed to acidic solutions. Further, there is a need for an improved method of preventing or limiting the corrosion of carbon and chrome steel goods exposed to acid solutions. Furthermore, there is a need for an acid corrosion inhibitor which will not cause crosslinking in polyacrylamide acid gels. Still further, there is a need for improved methods of acid stimulation of oil, gas and water wells which limits the corrosive effects of the stimulations on chrome and carbon steel components utilized in the wells.